/* Basic constants and macros */
#define WSIZE       4		/* Word and header/footer size (bytes) */
#define DSIZE       8		/* Double word size (bytes) */
#define CHUNKSIZE  (1<<2)	/* Extend heap by this amount (bytes) */

#define MAX(x, y) ((x) > (y)? (x) : (y))

/* Pack a size and allocated bit into a word */
#define PACK(size, alloc)  ((size) | (alloc))

/* Read and write a word at address p */
#define GET(p)       (*(unsigned int *)(p))
#define PUT(p, val)  (*(unsigned int *)(p) = (val))

/* Read the size and allocated fields from address p */
#define GET_SIZE(p)  (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)

/* Given block ptr bp, compute address of its header and footer */
#define HDRP(bp)       ((char *)(bp) - WSIZE)
#define FTRP(bp)       ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE)

/* Given block ptr bp, compute address of next and previous blocks */
#define NEXT_BLKP(bp)  ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE)))
#define PREV_BLKP(bp)  ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE)))

int mm_init(void)
{
	/* Create the initial empty heap */
	if ((heap_listp = mem_sbrk(4*WSIZE)) == (void *)-1)
		return -1;
	PUT(heap_listp, 0);				/* Alignment padding */
	PUT(heap_listp + (1*WSIZE), PACK(DSIZE, 1));	/* Prologue header */
	PUT(heap_listp + (2*WSIZE), PACK(DSIZE, 1));	/* Prologue footer */
	PUT(heap_listp + (3*WSIZE), PACK(0, 1));	/* Epilogue header */
	heap_listp += (2*WSIZE);

	/* Extend the empty heap with a free block of CHUNKSIZE bytes */
	if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
		return -1;
	return 0;
}

static void *extend_heap(size_t words)
{
	char *bp;
	size_t size;

	/* Allocate an even number of words to maintain alignment */
	size = (words %2) ? (words+1) * WSIZE : words * WSIZE;
	if ((long)(bp = mem_sbrk(size)) == -1)
		return NULL;

	/* Initialize free block header/footer and the epilogue header */
	PUT(HDRP(bp), PACK(size, 0));		/* Free block header */
	PUT(FTRP(bp), PACK(size, 0));		/* Free block footer */
	PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1));	/* New epilogue header */

	/* Coalesce if the previous block was free */
	return coalesce(bp);
}

void mm_free(void *bp)
{
	size_t size = GET_SIZE(HDRP(bp));

	PUT(HDRP(bp), PACK(size, 0));
	PUT(FTRP(bp), PACK(size, 0));
	coalesce(bp);
}

static void *coalesce(void *bp)
{
	size_t prev_alloc = GET_ALLOC(FTRP(PREV_BLKP(bp)));
	size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
	size_t size = GET_SIZE(HDRP(bp));

	if (prev_alloc && next_alloc) {			/* Case 1 */
		return bp;
	} else if (prev_alloc && !next_alloc) {		/* Case 2 */
		size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
		PUT(HDRP(bp), PACK(size, 0));
		PUT(FTRP(bp), PACK(size, 0));
	} else if (!prev_alloc && next_alloc) {		/* Case 3 */
		size += GET_SIZE(HDRP(PREV_BLKP(bp)));
		PUT(FTRP(bp), PACK(size, 0));
		PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
		bp = PREV_BLKP(bp);
	} else {
		size += GET_SIZE(HDRP(PREV_BLKP(bp))) +
			GET_SIZE(FTRP(NEXT_BLKP(bp)));
		PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
		PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
		bp = PREV_BLKP(bp);
	}
	return bp;
}

void *mm_malloc(size_t size)
{
	size_t asize;		/* Adjusted block size */
	size_t extendsize;	/* Amount to extend heap if no fit */
	char *bp;

	/* Ignore spurious requests */
	if (size == 0)
		return NULL;

	/* Adjust block size to include overhead and alignment reqs. */
	if (size <= DSIZE)
		asize = 2*DSIZE;
	else
		asize = DSIZE * ((size + (DSIZE) + (DSIZE-1)) / DSIZE);

	/* Search the free list for a fit */
	if ((bp = find_fit(asize)) != NULL) {
		place(bp, asize);
		return bp;
	}

	/* No fit found. Get more memory and place the block */
	extendsize = MAX(asize, CHUNKSIZE);
	if ((bp = extend_heap(extendsize/WSIZE)) == NULL)
		return NULL;
	place(bp, asize);
	return bp;
}

static void *find_fit(size_t asize)
{
	/* First-fit search */
	void *bp;

	for (bp = heap_listp; GET_SIZE(HDRP(bp)) > 0; bp = NEXT_BLKP(bp)) {
		if (!GET_ALLOC(HDRP(bp)) && (asize <= GET_SIZE(HDRP(bp)))) {
			return bp;
		}
	}
	return NULL; /* No fit */
}

static void place(void *bp, size_t asize)
{
	size_t csize = GET_SIZE(HDRP(bp));

	if ((csize - asize) >= (2*DSIZE)) {
		PUT(HDRP(bp), PACK(asize, 1));
		PUT(FTRP(bp), PACK(asize, 1));
		bp = NEXT_BLKP(bp);
		PUT(HDRP(bp), PACK(csize-asize, 0));
		PUT(FTRP(bp), PACK(csize-asize, 0));
	} else {
		PUT(HDRP(bp), PACK(csize, 1));
		PUT(FTRP(bp), PACK(csize, 1));
	}
}
